Linux Command Chaining: A Comprehensive Guide

Command chaining in POSIX-compliant Linux shells (such as bash, zsh, and sh) allows users to execute multiple commands sequentially or conditionally using specific operators. This powerful feature enhances automation and script efficiency. Below, we explore different chaining operators and their practical applications.

Command Chaining Operators

1. Semicolon (`;`)

• Runs commands sequentially, regardless of success or failure.

  command1 ; command2 ; command3
  

2. Logical AND (`&&`)

• Executes the next command only if the previous one succeeds (exit code 0).

  command1 && command2 && command3
  

3. Logical OR (`||`)

• Runs the next command only if the previous one fails (non-zero exit code).

  command1 || command2 || command3
  

4. Pipe (`|`)

• Redirects the output of one command as input to another.

  command1 | command2 | command3
  

5. Grouping Commands (`{}` or `()`)

• Combines commands into a block for conditional execution.

  { command1 && command2; } || command3
  

or

(command1 && command2) || command3

You Should Know: Practical Examples

1. Conditional Execution in Scripts

mkdir /backup && cp -r /data /backup || echo "Backup failed!"

#### **2. Error Handling with `||`**

ping -c 1 google.com || { echo "Network down!"; exit 1; }

#### **3. Sequential Tasks with `;`**

apt update ; apt upgrade -y ; reboot

#### **4. Combining `&&` and `||`**

grep "error" /var/log/syslog && echo "Errors found!" || echo "No errors."

#### **5. Piping Output for Processing**

cat /var/log/auth.log | grep "Failed" | wc -l

#### **6. Command Grouping for Complex Logic**

{ [ -f /tmp/lock ] && rm /tmp/lock; } || touch /tmp/lock

### **What Undercode Say**

Command chaining is essential for efficient Linux scripting and system administration. Mastering these operators allows for:
– Automated workflows (e.g., backups, updates).
– Error handling (e.g., fallback actions).
– Log parsing (e.g., filtering logs with `grep` and awk).

For further learning, visit:

• Linux Command Chaining Guide

### **Expected Output:**

<h1>Example: Backup script with chaining</h1>

tar -czf /backup/data.tar.gz /data && \
echo "Backup successful" || \
echo "Backup failed" > /var/log/backup.log

(End of article)

References:

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